Pain sensitization is an adaptive response to tissue injury because it fosters behaviors that protect the site of injury while it heals. Sensitization cn occur across multiple sensory modalities such as thermal and mechanical and can manifest as responsiveness to previously non-noxious stimuli (allodynia) or exaggerated responsiveness to noxious stimuli (hyperalgesia). My laboratory has been modeling the thermal mode of nociceptive sensitization in Drosophila larvae since precise quantitative assays for this mode have been developed and refined. Clinically, however, mechanical hypersensitivity following tissue trauma, surgery, or in a variety of disease states that cause chronic pain (such as cancer and diabetes) is a more serious problem than the thermal mode. This is because patients encounter mechanical stimulation much more commonly in the course of daily life. Our goal in this R21 proposal is to develop the assays and tools and a sufficient basic genetic depth of understanding for the field to begin to dissect mechanical pain hypersensitivity in Drosophila. Our guiding hypothesis is that there is conserved molecular genetic machinery that initiates, regulates, executes, and terminates mechanical nociceptive sensitization. We have developed customized Von Frey filaments suitable for testing mechanical nociceptive responses in Drosophila larvae, have defined the precise noxious range for these animals, and have demonstrated the existence of mechanical allodynia and hyperalgesia following UV-induced tissue injury. Further, in a small-scale pilot screen we have identified a small number of genes required for mechanical nociception. Our project goals are enumerated in the following specific aims: 1. To test the hypothesis that particular types of tissue damage (physical wounding, burns, chemotherapy) are more potent at inducing mechanical nociceptive hypersensitivity. 2. To test the hypothesis that mechanical nociceptive hypersensitivity uses the same inducing signals as thermal nociceptive hypersensitivity. And, 3. To characterize novel genes required for mechanical nociceptive sensitization. This project represents the first systematic study of mechanical nociceptive sensitization in a model genetic organism and has great potential for uncovering the genes that initiate, execute, and regulate this process. It uses a template that we have already used successfully in our approach to studying thermal nociceptive sensitization. Given the conservation of genes required for most fundamental neuronal functions we expect that this project will inform our understanding of mechanical nociceptive sensitization in vertebrates and in pathophysiological states, such as cancer, diabetes, and chronic pain syndromes, where this form of sensory neuron plasticity is thought to be improperly activated or regulated.